Akai MPK49 Pad Modification

A few years ago I did a light review of the Akai MPK49 MIDI keyboard controller. Subsequently I bought one and I've been happily using it since.

However one thing consistently bugged me (and everyone else) about the design - the drum "pads" are terrible. You have to hit them quite hard to even register a hit, let alone a loud one. Because I'd never really used such pads before, it didn't bother me too much. But Kong is coming...

So when I saw these two threads on the Propellerhead User Forum, I knew I had to give this a try. I'm really glad I did.

This video is a nice guide on how to take the MPK49 apart and get access to the rubber pads. There are 28 screws to remove, but it's not very difficult. The video author does a good job showing how to get inside, so I'm not going to rehash that here.

Some things to remember while taking apart your precious MIDI controller:

• use a manual screwdriver rather than a motorised one as in the video - take note of how much torque is required to unscrew those twenty rear-plate screws, and when you put back together again, do not tighten them up any more than that. You're screwing into plastic - you do NOT want to strip the threads!
• also try not to cross the threads when you're putting the screws back in, or you'll risk stripping the threads.
• when you remove the little PCB, watch out for that little 1-inch ribbon connector. It's not too fragile I suspect, but try not to pull on it if you can.
• when removing or replacing the rubber pads, be careful not to damage or scratch the underlying sensor array. I don't know exactly what it is (PVDF perhaps?) but it looks delicate.
• when you replace the outer case, be careful not to trap the ribbon cables that might stick out the back.

 
The fundamental problem with the pads is that there is a gap of approximately 1mm between the bottom of each pad and the pressure sensor underneath. This means you have to hit or press the pad hard enough to travel that 1mm before any pressure will be sensed, regardless of the pad sensitivity settings within the MPK49. It doesn't matter how sensitive you set the software within the keyboard to be, that gap is always going to be a problem.

The simple solution is to fill the gap up with something. Many people, including that video, recommend using four layers of electrical insulation tape underneath the rubber pads. But electrical insulation tape? Really? I hate that stuff! After a while, the adhesive oozes out and goes everywhere, it's horrible, horrible stuff. Avoid!

Instead, I decided to use some cloth tape, sometimes rightly or wrongly called "duct tape", or occasionally "gaffer tape" (although mine isn't black nor has it a matte finish). The nice quality about this tape is that the adhesive is pretty stable and doesn't migrate much, but it's also pretty sticky. It's also quite robust and for this application it should hold its thickness over time.

I didn't know how much I'd need initially so I put a strip onto some grease-proof baking paper and ruled out 15mm x 24mm rectangles. The baking paper made it really easy to cut the tape to the right size and then peel it off for application without contaminating the glue with dust or clothing lint.

I started off with just a single layer on a single pad. I reinstalled the rubber pads and gave it a try. The improvement was considerable - in fact I was very tempted to leave it at that. But of course I'm not one to take something apart without trying out a few things...

So I tried two layers. This was even better! I could now do cool drum rolls with my fingers and I wasn't constantly 'missing' the pads and sounding incompetent.

Once again, I was going to leave it at two layers, but just to make sure I tried out a few pads with three layers.

Wow! The improvement is dramatic! I barely have to exert any pressure on the pads at all to get a decent signal, yet I don't get spurious hits either. Three layers is definitely where it's at in my opinion.

But three layers of the tape I've got doesn't mean much to anyone else, so I measured it for you.

Without going into the gory details, I ascertained that the tape is approximately 0.3mm thick, and I used three layers, so that's a total thickness of 0.9mm, with an error of, let's say, +/- 0.05mm. When you look at the underside of the rubber pads end-on, you can see the top layer of tape just below the edge.

(I used the coin as a known thickness to measure inside the pad cavity - the coin is 2.15mm thick on the edge, I measured 8.05mm without tape, and 8.97mm with three layers of tape. This is about 0.3mm per layer.)

Once you've put it all back together, you can set the pad sensitivity, threshold and curves to whatever you want. I'm using threshold 1, sensitivity 16, curve A and it seems to work fine.

The Akai MPK49 is a great but not perfect keyboard. If you have one, I definitely recommend doing this mod - it's not hard, just take your time and think ahead. In total it took me about an hour with all the measuring, experiments, etc.

Bring on Kong!